A wavelength stability monitoring device and method and a control method for a laser

Abstract

The application discloses a wavelength stability monitoring device and method and a laser control method, and solves the problem of poor long-time measurement wavelength stability of a micro-displacement measurement mirror group, and specifically comprises a light splitting prism, a polarization light splitting prism, a first quarter-wave plate, a second quarter-wave plate, a first mirror and the like, wherein the first side and the third side are opposite to each other, and the second side and the fourth side are opposite to each other; the light splitting prism and a back reflection prism are arranged on the first side; the first quarter-wave plate and the first mirror are arranged on the third side; the second quarter-wave plate and the second mirror are arranged on the second side; a right-angle prism is arranged on the fourth side; a first photoelectric receiver and a second photoelectric receiver are arranged at a gap between the light splitting prism and the back reflection prism, the first photoelectric receiver is used for acquiring a 12-fold frequency actual measurement signal; the second photoelectric receiver is used for acquiring an 8-fold frequency actual measurement signal; and a displacement acquisition card is connected with the first photoelectric receiver, the second photoelectric receiver and an upper computer respectively.

Description

TECHNICAL FIELD

[0001] The present application relates to a laser wavelength monitoring device and method, in particular to a wavelength stability monitoring device and method and a laser control method. BACKGROUND

[0002] The laser micro displacement sensor takes the laser wavelength as the reference, and is the most important non-contact measurement tool for sub-nanometer measurement or even picometer measurement, and can be widely applied to the fields of ultra-precision equipment processing and manufacturing and precision measurement. In the laser displacement measurement, the wavelength stability will determine the accuracy of the measurement result of the laser micro displacement sensor. For example, the photolithography machine representing the highest level in the field of ultra-precision processing needs the laser micro displacement sensor to measure the logic chip with a processing precision of 5nm and 3nm for 32nm and 13nm, and therefore the high-stability laser wavelength is an essential condition for realizing ultra-precision measurement.

[0003] There are many factors affecting the laser wavelength stability. One is the temperature change, mechanical vibration, sound wave and pressure during the transmission of the laser, which causes the disturbance of the laser wavelength during the transmission. The other is the optical mixing caused by the mirror reflection, reference arm and measurement arm frequency component in the optical structure, which introduces the nonlinear error. In order to solve the above problems, many scholars at home and abroad have carried out in-depth research in this regard. The research team of Harbin Institute of Technology starts from the double-frequency laser itself, and uses the double-longitudinal-mode method and the frequency locking method for frequency stabilization. The 7714 and 7722 series of Zygo company use water-cooled heat dissipation method for frequency stabilization, or use single acousto-optic modulation method for double-frequency development. The NGI series of keysight company uses the integrated mirror group to form the mirror group, but these cannot completely eliminate the problem of laser wavelength fluctuation in the actual micro displacement sensor measurement.

[0004] For the problem of laser transmission wavelength stability control in the existing micro displacement sensor measurement, no matter from which aspect the laser wavelength stability is monitored, the measurement precision is limited due to the fact that the real-time measurement of the nonlinear error of the optical structure and the environmental disturbance error cannot be considered at the same time. Therefore, it is necessary to provide a laser wavelength monitoring device with high reliability and real-time feedback monitoring. SUMMARY

[0005] The purpose of the present application is to provide a wavelength stability monitoring device and method and a laser control method, so as to solve the technical problem of poor wavelength stability in long-time measurement of the existing micro displacement measurement mirror group, which leads to insufficient displacement measurement precision.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] The application relates to a wavelength stability monitoring device, which is characterized in that the device comprises a light splitting prism, a polarization light splitting prism, a first quarter-wave plate, a second quarter-wave plate, a first mirror, a second mirror, a right-angle prism, a back reflection prism, a first photoelectric receiver, a second photoelectric receiver, a displacement acquisition card and an upper computer.

[0008] The polarization light splitting prism is rectangular, the first side and the third side are opposite to each other, and the second side and the fourth side are opposite to each other.

[0009] The light splitting prism and the back reflection prism are sequentially arranged on the first side of the polarization light splitting prism along the length direction of the polarization light splitting prism, and a gap for emitting light is arranged between the light splitting prism and the back reflection prism; the light splitting prism is used for receiving a laser to be monitored and performing energy splitting to form two parallel light beams which are incident on the polarization light splitting prism; the laser to be monitored is orthogonal linearly polarized light.

[0010] The first quarter-wave plate and the first mirror are sequentially arranged on the third side of the polarization light splitting prism in a direction away from the polarization light splitting prism.

[0011] The second quarter-wave plate and the second mirror are sequentially arranged on the second side of the polarization light splitting prism in a direction away from the polarization light splitting prism.

[0012] The right-angle prism is arranged on the fourth side of the polarization light splitting prism, and the bottom side of the right-angle prism is arranged close to the polarization light splitting prism.

[0013] The first photoelectric receiver and the second photoelectric receiver are arranged at the gap between the light splitting prism and the back reflection prism, and the detection ends of the two photoelectric receivers correspond to two light beams emitted from the gap respectively; the first photoelectric receiver is used for acquiring a 12th harmonic measured signal; and the second photoelectric receiver is used for acquiring an 8th harmonic measured signal.

[0014] The input end of the displacement acquisition card is connected with the output ends of the first photoelectric receiver and the second photoelectric receiver respectively, and the output end of the displacement acquisition card is connected with the upper computer.

[0015] Further, the light splitting prism comprises a BS light splitting prism and a third mirror which are arranged side by side along the thickness direction of the polarization light splitting prism.

[0016] Further, the back reflection prism comprises a first back reflection prism and a second back reflection prism which are arranged side by side along the thickness direction of the polarization light splitting prism.

[0017] The first back reflection prism is used for receiving light from the BS light splitting prism and reflecting the light to the polarization light splitting prism.

[0018] The second back reflection prism is used for receiving light emitted from the third mirror and reflecting the light to the polarization light splitting prism.

[0019] Further, the device further comprises a displacement stage.

[0020] The displacement table acting end is connected with the second mirror, and is used for micro-displacing the second mirror.

[0021] A wavelength stability monitoring method, which is characterized by comprising the following steps:

[0022] Step 1, using the above wavelength stability monitoring device to monitor the laser to be monitored, the first photoelectric detector acquires a 12th harmonic measured signal, and the second photoelectric receiver acquires an 8th harmonic measured signal;

[0023] Step 2, the 12th harmonic measured signal and the 8th harmonic measured signal are normalized and data-fitted respectively to obtain a 12th harmonic measurement error and an 8th harmonic measurement error;

[0024] Step 3, the 12th harmonic measurement error and the 8th harmonic measurement error are subtracted to obtain a 4th harmonic optical subdivision optical path transmission measurement error;

[0025] Step 4, the 12th harmonic measurement error is multiplied by 3 to obtain 12th harmonic corrected signal error information, and the 8th harmonic measurement error is multiplied by 2 to obtain 8th harmonic corrected signal error information;

[0026] Step 5, it is judged whether the 12th harmonic corrected signal error information and the 8th harmonic corrected signal error information are within ±2ppb, and whether the 12th harmonic measurement error fluctuation is lower than 1ppb;

[0027] If the 12th harmonic corrected signal error information and the 8th harmonic corrected signal error information are within ±2ppb, and the 12th harmonic measurement error fluctuation is lower than 1ppb, the current 12th harmonic measurement error is the wavelength stability monitoring signal of the laser to be monitored;

[0028] If one of the 12th harmonic corrected signal error information and the 8th harmonic corrected signal error information is outside the range of ±2ppb, or the 12th harmonic measurement error fluctuation is equal to or higher than 1ppb, step 6 is executed;

[0029] Step 6, the 12th harmonic corrected signal error information and the 8th harmonic corrected signal error information are used as correction files and uploaded to a laser used for emitting the laser to be monitored to correct the light emitted by the laser; returning to step 1 until the 12th harmonic corrected signal error information and the 8th harmonic corrected signal error information are within ±2ppb, and the 12th harmonic measurement error fluctuation is lower than 1ppb, and the current 12th harmonic measurement error is the wavelength stability monitoring signal of the laser to be monitored.

[0030] A laser control method, which is characterized by comprising the following steps:

[0031] Step 1: Obtain wavelength stability monitoring signals using the wavelength stability monitoring method described above;

[0032] Step 2: Divide the obtained wavelength stability monitoring signal by 4, and at the same time obtain the initial wavelength parameters of the laser. Extract the integer and decimal values ​​of the initial wavelength parameters of the laser.

[0033] Step 3: Based on laser interference theory and Doppler frequency shift theory, the integer and fractional wavelength values ​​are corrected using the wavelength stability monitoring signal after dividing by 4 to obtain the real-time laser correction wavelength.

[0034] Step 4: Use the real-time laser correction wavelength as the actual wavelength of the laser to make the laser output the laser to be monitored.

[0035] The beneficial effects of this invention are:

[0036] 1. Compared with existing technologies, this invention highlights the high-precision real-time feedback identification measurement with the same optical path and structure at the same level. It uses the same frequency feedback method to construct a two-layer measurement structure with different frequency harmonics. It does not require additional frequency stabilization processing of the dual-frequency laser itself. Instead, it performs real-time measurement and monitoring of laser wavelength stability on the basis of its frequency stabilization. By optimizing the measurement error of the frequency doubling measurement system in real time, it establishes a system that simultaneously takes into account displacement measurement with different fineness and high stability measurement. It can not only accurately control the wavelength change state of the laser in different times and under different environments, but also obtain ultra-precise laser displacement measurement accuracy.

[0037] 2. The wavelength stability monitoring device of the present invention provides a dual-layer structure of 8th harmonic laser measurement and 12th harmonic laser measurement. The 8th harmonic laser can be used as a coarse optical ruler, and the 12th harmonic laser can be used as a fine optical ruler, so as to realize coarse and fine measurements at the same level, making the measurement results more accurate.

[0038] 3. The wavelength stability monitoring device of the present invention not only facilitates miniaturization and integration, but also takes into account the installation control and positioning issues of micro-displacement sensors.

[0039] 4. The present invention also provides a displacement stage for the second reflector, thereby enabling displacement measurement. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of an embodiment of the wavelength stability monitoring device of the present invention;

[0041] Figure 2 This is a flowchart of an embodiment of a wavelength stability monitoring method according to the present invention;

[0042] Figure 3 This is a flowchart of an embodiment of a laser control method according to the present invention.

[0043] Reference Signs:

[0044] 1-laser, 2-splitting prism, 3-polarization splitting prism, 401-first quarter wave plate, 402-second quarter wave plate, 501-first mirror, 502-second mirror, 6-right-angle prism, 7-retro-reflective prism, 701-first retro-reflective prism, 702-second retro-reflective prism, 801-first photoelectric receiver, 802-second photoelectric receiver, 9-displacement stage, 10-displacement acquisition card, 11-upper computer. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0046] The wavelength stability monitoring device provided by the embodiments of the present application forms a corresponding two-layer multi-point incident mode by using a double incident optical structure, and realizes accurate measurement of the error of laser wavelength in the transmission process in super-precision displacement measurement by using an optical path structure that is completely consistent and differs by four times in optical subdivision. The device is divided into two layers, one of which is an 8-fold frequency displacement measurement structure, and the other is a 12-fold frequency displacement measurement structure. A 632.8 nm double-frequency laser is incident, and the transmitted light is incident to the 12-fold frequency displacement measurement structure after being split by a splitting prism 2, and forms a 12-fold frequency measured signal after 6 times of round-trip motion and being incident to a photoelectric receiver. The reflected light is incident to the 8-fold frequency displacement measurement structure after 4 times of round-trip motion, and forms an 8-fold frequency measured signal after being incident to the photoelectric receiver. Since the 12-fold frequency displacement measurement structure and the 8-fold frequency displacement measurement structure not only meet the same optical path and common optical path in the optical path structure, but also have consistent structures and consistent optical paths, the error value of the 8-fold frequency displacement measurement can be subtracted from the error value of the 12-fold frequency displacement measurement, and the laser transmission error value in the multiple round-trip states can be obtained. Then, the error value is expanded to the same multiple on the basis of the error value, and the to-be-monitored laser is optimized in real time, so that it is more stable. The device not only realizes the miniaturization design of the micro-displacement sensor through the flat structure, but also obtains high-precision displacement measurement of optical rulers with different thicknesses and accuracies, and provides a new device for manufacturing and precision assembly of high-end manufacturing.

[0047] Specifically, as Figure 1As shown, the wavelength stability monitoring device comprises a beam splitter prism 2, a polarization beam splitter prism 3, a first quarter-wave plate 401, a second quarter-wave plate 402, a first mirror 501, a second mirror 502, a right-angle prism 6, a retroreflective prism 7 (the retroreflective prism 7 comprises a first retroreflective prism 701 and a second retroreflective prism 702), a first photoelectric receiver 801, a second photoelectric receiver 802, a displacement acquisition card 10, and an upper computer 11; wherein the beam splitter prism 2, the polarization beam splitter prism 3, the first quarter-wave plate 401, the second quarter-wave plate 402, the first mirror 501, the second mirror 502, the right-angle prism 6, and the first retroreflective prism 701 constitute a 12-fold displacement measurement structure, and the beam splitter prism 2, the polarization beam splitter prism 3, the first quarter-wave plate 401, the second quarter-wave plate 402, the first mirror 501, the second mirror 502, the right-angle prism 6, and the second retroreflective prism 702 constitute an 8-fold displacement measurement structure.

[0048] The beam splitter prism 2 is a BS beam splitter prism and a third mirror cemented body, used for forming a two-layer measurement structure; the first quarter-wave plate 401 and the second quarter-wave plate 402 are used for changing the polarization state of light; the first mirror 501 is used for reference, as a reference mirror, and the second mirror 502 is used for measurement, as a measurement mirror; the first retroreflective prism 701 and the second retroreflective prism 702 are used for retroreflecting light; the first photoelectric receiver 801 and the second photoelectric receiver 802 are used for receiving measurement signals and reference signals to obtain interference signals; the displacement stage 9 is used for micro-displacement moving the second mirror 502; the displacement acquisition card 10 is connected with the first photoelectric receiver 801 and the second photoelectric receiver 802, and is used for real-time acquisition of displacement measurement signals of the first photoelectric receiver 801 and the second photoelectric receiver 802; the output end of the displacement acquisition card 10 is connected with the upper computer 11, and the upper computer 11 is used for displaying an 8-fold pre-correction measured signal, a 12-fold pre-correction measured signal, a wavelength real-time change signal, an 8-fold post-correction measured signal, and an initial parameter of the laser.

[0049] In this embodiment, the laser 1 used for outputting the laser to be monitored is a dual-frequency laser, the dual-frequency laser emits an orthogonal linearly polarized light, the first energy splitting of the light is performed by the beam splitter prism 2, the transmitted light is a first incident light beam, and the reflected light is a second incident light beam;

[0050] The first incident light beam passes through the 12-fold displacement measurement structure, is incident to the first photoelectric detector 801, is photoelectrically converted by the displacement acquisition card 10, converts optical measurement information into electrical voltage information, is amplified and filtered, and is finally displayed on the upper computer 11;

[0051] The second incident light beam is incident to the second photodetector 802 through the 8 times frequency shift measurement structure, is photoelectrically converted by the displacement acquisition card 10, converts the optical measurement information into electrical voltage information, is amplified and filtered, and is finally displayed on the host computer 11.

[0052] The first incident light beam is split by the polarizing beam splitter 3 into transmitted light and reflected light. The transmitted light is transmitted by the first quarter wave plate 401, reflected by the first mirror 501, returns to the original path, changes the polarization state, is reflected by the polarizing beam splitter 3, is twice reflected by the right-angle prism 6, is reflected by the polarizing beam splitter 3, is transmitted by the first quarter wave plate 401, is reflected by the first mirror 501, returns to the original path, changes the polarization state, is transmitted by the polarizing beam splitter 3, is twice reflected by the first retroreflective prism 701, is transmitted by the polarizing beam splitter 3, is transmitted by the first quarter wave plate 401, is reflected by the first mirror 501, returns to the original path, changes the polarization state, is reflected by the polarizing beam splitter 3, is twice reflected by the right-angle prism 6, is reflected by the polarizing beam splitter 3, is transmitted by the first quarter wave plate 401, is reflected by the first mirror 501, returns to the original path, changes the polarization state, is transmitted by the polarizing beam splitter 3, is twice reflected by the first retroreflective prism 701, is transmitted by the polarizing beam splitter 3, is transmitted by the first quarter wave plate 401, is reflected by the first mirror 501, returns to the original path, is reflected by the polarizing beam splitter 3, is twice reflected by the right-angle prism 6, is reflected by the polarizing beam splitter 3, is transmitted by the first quarter wave plate 401, is reflected by the first mirror 501, returns to the original path, changes the polarization state, is transmitted by the polarizing beam splitter 3, and forms a reference signal incident to the first photoreceiver 801. The reflected light and the transmitted light have the same optical path structure, are transmitted by the second quarter wave plate 402 six times and are reflected by the second mirror 502 six times, form a measurement signal, and are incident to the first photoreceiver 801.

[0053] The first photoreceiver 801 simultaneously receives the measurement signal and the reference signal, changes the polarization state, acquires an interference signal, and obtains a 12 times frequency real measurement signal.

[0054] The second incident light beam is split by polarizing beam splitter prism 3 into transmitted light and reflected light. The transmitted light is transmitted through the first quarter-wave plate 401, reflected by the first reflecting mirror 501, returns along the same path, changes its polarization state, is reflected by polarizing beam splitter prism, is reflected twice by right-angle prism 6, reflected by polarizing beam splitter prism 3, transmitted through the first quarter-wave plate 401, reflected by the first reflecting mirror 501, returns along the same path, changes its polarization state, is transmitted through polarizing beam splitter prism 3, is reflected twice by second retroreflection prism 702, is transmitted through polarizing beam splitter prism 3, and is then incident on the first quarter-wave plate 401. The transmitted light is reflected by the first reflecting mirror 501 and returns along the same path, changing its polarization state. It is then reflected by the polarizing beam splitter prism, reflected twice by the right-angle prism 6, reflected by the polarizing beam splitter prism 3, transmitted through the first quarter-wave plate 401, reflected by the first reflecting mirror 501, and returns along the same path, changing its polarization state. It is then transmitted through the polarizing beam splitter prism 3 to form a reference signal that is incident on the second photodetector 802. The reflected light and transmitted light have the same optical path structure. They are transmitted four times by the second quarter-wave plate 402 and reflected four times by the second reflecting mirror 502 to form a measurement signal that is incident on the second photodetector 802.

[0055] The second photoelectric receiver 802 simultaneously receives the measurement signal and the reference signal. By changing the polarization state, the interference signal obtained is the 8th harmonic measured signal.

[0056] The 12th harmonic displacement measurement structure and the 8th harmonic displacement measurement structure have the same principle and the same optical path. They differ by four times in optical subdivision, and the measured displacement is the same. However, the Doppler frequency shifts differ by 4Δf.

[0057] like Figure 2 As shown, this embodiment also provides a wavelength stability monitoring method, specifically:

[0058] The above wavelength stability monitoring device is used to process the laser to be monitored. The 12th harmonic measured signal obtained by the first photodetector 801 and the 8th harmonic measured signal obtained by the second photodetector 802 are displayed on the host computer 11. The 12th harmonic measured signal and the 8th harmonic measured signal are normalized and fitted, respectively, to obtain the 12th harmonic measurement error and the 8th harmonic measurement error. The two error data are obtained synchronously by sampling. The two-dimensional data are subtracted to obtain the optical path transmission frequency multiplication measurement error of the phase difference 4 times. Then, the frequency multiplication measurement error is multiplied by 3 to obtain the corrected 12th harmonic corrected signal error information, and the frequency multiplication measurement error is multiplied by 2 to obtain the corrected 8th harmonic corrected signal error information. The 12th harmonic corrected signal error information is used as a correction file and transmitted to the laser 1 to correct the error of the incident light, thereby obtaining the optimized 12th harmonic measured signal. The 8th harmonic corrected signal error information is used as a correction file and transmitted to the laser 1 to correct the error of the incident light, thereby obtaining the optimized 8th harmonic measured signal. Then, the optimized 12th harmonic measured signal is normalized and fitted again to obtain a new round of 12th harmonic measurement error. The optimized 8th harmonic measured signal is normalized and fitted again to obtain a new round of 8th harmonic measurement error. Finally, the new round of 12th harmonic measurement error and the new round of 8th harmonic measurement error are corrected. When the difference between the new round of 12th harmonic measurement error and the new round of 8th harmonic measurement error is almost negligible (the frequency stabilization accuracy of the obtained 12th harmonic measured signal and 8th harmonic measured signal is almost within ±2ppb, and the frequency multiplication measurement error fluctuation is lower than 1ppb), the high-precision laser wavelength stability monitoring signal is obtained.

[0059] As Figure 3 shown, the embodiment also provides a control method of a laser, specifically:

[0060] The high-precision laser wavelength stability monitoring signal is obtained by using the above wavelength stability monitoring method, the laser local oscillator wavelength information is displayed on the host computer 11 as the initial laser wavelength parameter, the wavelength stability monitoring signal is the 4 times laser wavelength transmission signal, and therefore the synchronous laser real-time wavelength transmission signal is divided by 4, and the wavelength integer value and the wavelength decimal value of the initial laser wavelength parameter are extracted respectively; according to the laser interference theory and the Doppler frequency shift theory, the wavelength stability monitoring signal after being divided by 4 is used to correct the laser wavelength integer value and the laser wavelength decimal value again, and the real-time laser corrected wavelength is obtained, the real-time laser corrected wavelength is used as the actual wavelength in the laser transmission measurement, and the laser 1 outputs more stable laser to be monitored. Then the new 12 times frequency measurement signal obtained by the first photoelectric detector 801 and the new 8 times frequency measurement signal obtained by the second photoelectric receiver 802 are displayed on the host computer 11 again, the two signals are subtracted and multiplied by 3 to obtain a new round of 12 times frequency measurement signal, and multiplied by 2 to obtain a new round of 8 times frequency measurement signal, through normalization processing and data fitting, a new round of 12 times frequency measurement error and a new round of 8 times frequency measurement error are displayed, and a final correction file is obtained, and the final correction file can also be used to correct other related optical equipment.

[0061] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any change or replacement within the technical scope disclosed by the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A wavelength stability monitoring device, characterized in that: It includes a beam splitter (2), a polarizing beam splitter (3), a first quarter-wave plate (401), a second quarter-wave plate (402), a first reflector (501), a second reflector (502), a right-angle prism (6), a retroreflection prism (7), a first photodetector (801), a second photodetector (802), a displacement acquisition card (10), and a host computer (11); The polarizing beam splitter (3) is rectangular, with its first and third sides facing each other and its second and fourth sides facing each other; The beam splitter (2) and the retroreflector (7) are sequentially arranged on the first side of the polarizing beam splitter (3) along the side length direction. A gap is provided between the beam splitter (2) and the retroreflector (7) for the outgoing light to pass through. The beam splitter (2) is used to receive the laser to be monitored and split its energy to form two parallel beams that are incident on the polarizing beam splitter (3). The laser to be monitored is orthogonally linearly polarized light. The first quarter-wave plate (401) and the first reflecting mirror (501) are sequentially arranged on the third side of the beam splitter (3) in a direction away from the polarizing beam splitter (3); The second quarter-wave plate (402) and the second reflecting mirror (502) are sequentially arranged on the second side of the beam splitter (3) in a direction away from the polarizing beam splitter (3); The right-angle prism (6) is set on the fourth side of the polarizing beam splitter (3), and the bottom edge of the right-angle prism (6) is set close to the polarizing beam splitter (3). The first photodetector (801) and the second photodetector (802) are disposed in the gap between the beam splitter (2) and the retroreflector (7), and their detection ends are respectively corresponding to the two beams of light emitted from the gap; the first photodetector (801) is used to acquire the 12th harmonic measured signal; the second photodetector (802) is used to acquire the 8th harmonic measured signal; The input terminal of the displacement acquisition card (10) is connected to the output terminals of the first photoelectric receiver (801) and the second photoelectric receiver (802), respectively, and its output terminal is connected to the host computer (11).

2. The wavelength stability monitoring device according to claim 1, characterized in that: The beam splitter (2) includes a BS beam splitter and a third reflecting mirror arranged side by side along the thickness direction of the polarizing beam splitter (3).

3. The wavelength stability monitoring device according to claim 2, characterized in that: The retroreflection prism (7) includes a first retroreflection prism (701) and a second retroreflection prism (702) arranged side by side along the thickness direction of the polarizing beam splitter (3); The first retroreflection prism (701) is used to receive light from the BS beam splitter and reflect it back to the polarizing beam splitter (3); The second retroreflection prism (702) is used to receive the light emitted from the third reflecting mirror and reflect it back to the polarizing beam splitter (3).

4. The wavelength stability monitoring device according to any one of claims 1-3, characterized in that: It also includes a displacement stage (9); The displacement stage (9) is connected to the second reflector (502) at its working end, and is used to micro-displace the second reflector (502).

5. A method for monitoring wavelength stability, characterized in that, Includes the following steps: Step 1: The wavelength stability monitoring device according to any one of claims 1-4 is used to monitor the laser to be monitored. The first photodetector (801) acquires the measured signal of the 12th harmonic, and the second photodetector (802) acquires the measured signal of the 8th harmonic. Step 2: Normalize and fit the measured signals of the 12th harmonic and the 8th harmonic respectively to obtain the measurement error of the 12th harmonic and the measurement error of the 8th harmonic. Step 3: Subtract the 12th harmonic measurement error and the 8th harmonic measurement error from the two-dimensional data to obtain the optical path transmission harmonic measurement error that differs by 4 times the optical subdivision. Step 4: Multiply the frequency multiplication measurement error by 3 to obtain the 12th-fold frequency correction signal error information, and simultaneously multiply the frequency multiplication measurement error by 2 to obtain the 8th-fold frequency correction signal error information; Step 5: Determine whether the error information of the 12th harmonic correction signal and the error information of the 8th harmonic correction signal are within ±2ppb, and determine whether the fluctuation of the harmonic measurement error is less than 1ppb; If the error information of the 12th harmonic correction signal and the error information of the 8th harmonic correction signal are both within ±2ppb, and the fluctuation of the harmonic measurement error is less than 1ppb, then the current harmonic measurement error is the wavelength stability monitoring signal of the laser to be monitored. If either the 12th-harmonic correction signal error information or the 8th-harmonic correction signal error information is outside the range of ±2ppb, or if the harmonic measurement error fluctuation is equal to or greater than 1ppb, then proceed to step 6. Step 6: Upload the error information of the 12th harmonic frequency correction signal and the error information of the 8th harmonic frequency correction signal as correction files to the laser (1) used to emit the laser to be monitored to correct the emitted light; return to step 1 until the error information of the 12th harmonic frequency correction signal and the error information of the 8th harmonic frequency correction signal are both within ±2ppb, and the fluctuation of the harmonic frequency measurement error is less than 1ppb. Then the current harmonic frequency measurement error is the wavelength stability monitoring signal of the laser to be monitored.

6. A method for controlling a laser, characterized in that, Includes the following steps: Step 1: Obtain the wavelength stability monitoring signal using the wavelength stability monitoring method described in claim 5; Step 2: Divide the obtained wavelength stability monitoring signal by 4, and at the same time obtain the initial wavelength parameters of the laser (1), and extract the integer value and the decimal value of the initial wavelength parameters of the laser respectively. Step 3: Based on laser interference theory and Doppler frequency shift theory, the integer and fractional wavelength values ​​are corrected using the wavelength stability monitoring signal after dividing by 4 to obtain the real-time laser correction wavelength. Step 4: Use the real-time laser correction wavelength as the actual wavelength of the laser (1) to make the laser (1) output the laser to be monitored.

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